


Dark Blue

by shou



Series: Faster the Current (and other tales) [1]
Category: Haikyuu!!
Genre: Alternate Universe, Alternate Universe - Merpeople, Childhood Friends, Dreams, Fluff, M/M, Magic, Mermaid Kageyama Tobio, Ocean magic, Short & Sweet, Sunsets
Language: English
Status: Completed
Published: 2018-03-05
Updated: 2018-03-05
Packaged: 2019-03-27 10:37:06
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,410
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13879089
Author URL: https://archiveofourown.org/users/shou/pseuds/shou
Summary: He's barely twelve years old when Shouyou meets a little mermaid with blue nails and a blue tail and a grumpy voice.-The mermaid was obviously skeptical. But his eyes were glued to Shouyou’s, and he mouthed his name silently before giving his own. “Tobio,” he said. “My name is Tobio.”





	Dark Blue

**Author's Note:**

> HERE IT IS KIDS! AS PROMISED: KAGEHINA FLUFF FT. THE OCEAN!!!  
> for the best experience, listen to this playlist while reading, cause i listened to it while writing:  
> https://8tracks.com/khristinasg/ocean-s-expedition
> 
> OKAY! so kagehina mermaid au, people!  
> plz be gentle with me  
> title is from the song "Dark Blue" by Jack's Mannequin bc it came up in my music while i was posting this  
> im on tumblr @4hoots

His grandfather’s beach house was Shouyou’s favorite spot in the world. It was tiny, just four rooms (a kitchen and a living room and a bathroom and a tiny bedroom), painted white but weather-beaten into grey, and full of little knick-knacks like sailing knots and old fishing lures and seashells and old maps hung in handmade wooden frames. The kitchen was always full of food, and the little wood stove was always toasty warm during the cooler nights. Shouyou’s mother had been taking his sister and him there every summer for as long as he could remember before Natsu was even born! 

The summer vacation of his first year of junior high was especially fun, but not because of anything he could have predicted.

It was late July, a month after his birthday, the weather was warm but not sweltering, and the ocean was calm with only a few white-capped waves. 

“Can I go down to the beach? Pretty please? I wanna watch the sunset!” the little redhead looked up at his mother with big, round eyes, pleading. “I’ll be back in a few minutes!”

His mother looked at her son with a small smile, nodding. “Just be back in time for bedtime, okay? And make sure to wear your sandals!” But her son was already running out the door, toy shovel and red, plastic bucket in his hand, and no sandals on his bare feet.

Shouyou sped down the grassy hill with reckless abandon, nearly tripping over a tuft of grass. He jumped over a drift log, high and dry and bleached by the sun. The rocks between the grassy hill and the sand made him slow down, squeaking and yelping as rocks and twigs jabbed into the soles of his bare feet. But he kept running, whooping with joy when his toes felt sand. He broke into a dead sprint, heading straight for the distant surf. Low tide caused the waves to retreat far enough Shouyou ran for longer than he liked till he was jumping into the waves, the cold water splashing up to soak the bottom hem of his shorts.

A particularly large wave crept up on him, and Shouyou fell back on his butt with a joyous laugh. His bucket and shovel with it went flying and landed in the white foam a few meters away. When the wave retreated back to where it came from, the bucket and shovel were taken with it, out to deeper water where Shouyou couldn’t follow. 

“Come on, waves!” he shouted, raising a small fist and shaking it at the waves. They only sparkled in the evening sun, almost like they were laughing at him. But Shouyou wouldn’t let something so small ruin the sunset. He could get another bucket and shovel. So instead of moping, he jumped up and skipped to just beyond the waterline, where he plopped down in the dry sand. The wind blew through his hair, turning it into an even bigger mess than it already was, and the dying sun warmed his rosy cheeks.

With his knees pulled to his chest, Shouyou watched the sun slowly sink lower and lower, watching how the light bounced off of every ripple in the sea. The water looked almost black compared to the silver-white of the light, and the sky above him began to sink into a pale lilac, which quickly turned to a mixture of violets and dark, grey-blues. The sun was quickly turning orange, even more orange than Shouyou’s hair, and burning the few clouds around it a vibrant gold. Shouyou wished he had his drawing pad and crayons with him, because then he could have tried to capture the sunset on white craft paper. But he didn’t, so he just sat back and rested his chin on his knees and enjoyed the view. 

His eyelids grew heavy as he watched the sun sink lower and lower until the last little sliver was slipping behind the horizon. The sky held the vibrant, warm hues of the sun for only a few minutes more, but before Shouyou even realized it, the sky was now completely blues and faded purples, the horizon behind him, towards the beach house, was darkening, and the first star could be seen. Yawning, Shouyou unfolded his legs and stood up, ready to turn back and return home where his futon and blanket and pillow were waiting. 

But as he was turning to leave, something knocked into the back of his heel. Shouyou turned to look at the mystery object and gasped in happy surprise when he saw his little plastic bucket, bright red against the dull sand. He looked back to the ocean, squinting in suspicion. But he did pick the bucket up. The shovel was still attached by the little plastic loop through its handle.

“Did you bring my bucket back, waves?” he asked nobody in particular. He looked at his bucket a little more closely and noticed what looked almost like a small bite mark. Natsu probably got ahold of it without Shouyou noticing. “Well, thank you!” he called out. 

The ocean did not exactly respond, but a little wave did run up and lap at his ankles. 

“I have to go home now, waves,” he told the water. He lifted his foot carefully out of the chilly water and turned to continue on his way back to the grassy hill.

Another little wave reached him before he reached safety, and the ocean seemed to be pouting as the wave ran back to the surf, little bubbles following its border. 

“You can’t have my bucket!” Shouyou shook the thing at the waves, then turned and dashed back to the rocks and the grass, ignoring the way the waves seemed to chase him up to the dry sand, the seafoam leaving a shadowy line of its efforts to capture the small boy. 

Shouyou hopped across the rocks, ran up the grassy hill, and quietly slipped through the door and into the little house. His mother was sitting on the small rocking chair, reading a book by a dim light of the lamp on the bookshelf. 

“Your sister is already asleep,” she murmured. “Please be quiet while brushing your teeth.” She went back to her book, slowly rocking back and forth. 

“Yes, ma'am!” Shouyou mock-saluted and bowed, which made his mother laugh quietly into her book. “Goodnight!” He tiptoed over to her for a goodnight kiss, then tiptoed to the little bathroom attached to the bedroom. He didn’t turn on the light, since Natsu was asleep on the futon next to his mom’s, so he had to brush his teeth and change into pajamas all in the dark. There was some light coming in through the open window and the glass door, but not much. He yanked a brush through his unruly hair, rubbed his face with a warm, damp hand towel, then crawled under the thick blanket and curled around his pillow. 

The bedroom had a sliding glass door which was now rusted shut and couldn’t open, but had a perfect view of the beach, and therefore had a perfect view of the ocean. The water was dark, save for a few flashes of light from the houses along the shore and one or two boats, but the moon wasn’t out yet, and the stars were still too dim to reflect in the water. 

With the sound of the light wind outside and the distant din of the surf from the open window, Shouyou drifted into a happy, content, comfy sleep. 

 

_A flash of red caught his eye. Distinctly not of his world, it looked like one of the toys the little humans used when they shaped the wet piles of sand. He reached out to grab the object, pulling it down under his waves. It was smooth and hard, but when he brought it to his mouth and bit down, he could feel his sharp teeth make a mark on the odd material._

_The shape of a single little human caught his eye. The silhouette of the little human was familiar. The starfish shape of his hair, the bright color the same hue of the foreign fish and fancy, expensive coral jewelry his older brothers enjoyed wearing… This little human he had been seeing for many years now. He watched from under the waves as the little human shook an arm at the ocean before sitting down with his face to the sky. Now,_ this _he understood. The sun was beautiful, after all. Warm and brighter than any fish or coral he had seen…_

_From under the waves he watched the sun sink towards him, down into the dark unknown, the deep waters he was strictly forbidden from exploring, no matter how much he wanted to. Soon, the sun was gone, and the sky was too dim for him to see much above the surface. But he did see the little human because his hair was almost as bright as the sun itself. He would recognize that hair anywhere. He saw the little human get up and turn away._

_He looked down at the strange object floating between his hands, then made up his mind. With a small push of his palms from his chest, he sent the object along a small current and back up to the surface, bobbing along to the little human’s feet. He watched the human pick it up, and he listened to the little human speak to the waves. His waves, he wanted to say, but all he could do was make the smaller waves try to pull the little human into the water, into the depths where he could then investigate the little human._

_But he could not. So he let the little human go, and when he was out of sight and he could not hear any trace of his footsteps, he swam up to the shoreline, poking his head out of the water, swimming all the way up to where he was lying on his stomach on the soothing wet sand. It felt amazing against his scales, and he wriggled, digging his tail into the wet sand. The waves lapped around him, and he propped his head up on both hands._

_The little human was nearly asleep now. He could tell. He was good at sensing that little human._

_Turning his focus away from the little human, he rolled onto his back and pillowed his head on his arms. The stars would be coming out soon, and he would greet them with a proper song._

 

Shouyou woke up with a gasp, sitting bolt upright. His heart was pounding, his chest was heaving, gasping for air. It was as if something stole his breath. Beside him, Natsu was curled up in her blanket, and his mom was on the other side of her. The moon was high in the sky above the sea, casting pale, silver light in through the glass doors. Shouyou wasn’t sure what woke him up, he just knew _something_ had pulled him back to consciousness. 

The wind outside was quiet, and the ocean looked calm and glassy. Something was pulling at Shouyou. Something was telling him to get up and tiptoe out of the bedroom and through the kitchen to unlock the door and creep outside. He didn’t even realize he was listening to the strange calling until he was standing outside atop the grassy hill, looking out over the beach. His pajamas were enough to keep him warm in the night air, and he rubbed his eyes a little sleepily to try and wake up.

Everything around him was quiet, save for the quiet murmur of the waves at the waterline. Shouyou walked slowly across the hill, the grass cool and soft underneath his bare feet. As he was walking down the hill towards the sand, he noticed something sparkle at the waterline. He wasn’t close enough to see it properly, so he picked up his pace and ran the rest of the way down the hill and over the rocks and sand. But as he started running on the sand, something near the sparkly object moved. It looked sort of like a seal, but Shouyou couldn’t tell. 

He slowed down to roll up his pajama pants so they wouldn’t get wet, then carefully walked towards the mystery creature. He was close enough to see a sparkly fishtail, which was the thing that caught his eye from on top of the hill. The moonlight shone off of it in a beautiful iridescent display, and Shouyou’s eyes were wide with wonder. He crouched down to inspect the tail, but kept a couple meters away for safety’s sake. 

“What are you looking at, little human?” 

The voice startled Shouyou, and his gaze snapped up to the very human-like face attached to the bare torso attached to the sparky fish tale, propped up on one arm and staring at Shouyou.

“W-what?!” he squeaked, eyes glued to the mermaid- _mermaid!-_ ’s face. His face was very pretty, Shouyou thought. His hair was dark, more blue than black, and shone almost like his tail. The mermaid’s skin was so pale it looked almost translucent in the moonlight, and his eyes were so dark they looked almost black, looking at Shouyou from under long, dark lashes. Without a single doubt, the mermaid was the prettiest creature Shouyou had ever seen. 

“Can you speak, little human?” the mermaid asked, and while his face was beautiful, his voice was kind of harsh. He was glaring at Shouyou, mouth twisted in a grimace, revealing sharp, pearly teeth.

“I can speak!” he quickly answered. He crawled closer, ignoring the water and sand clinging to the knees of his pajama pants. So much for keeping them dry. “Are you a mermaid?” he asked. “‘Cause you look exactly like a mermaid!” 

The mermaid narrowed his eyes at Shouyou. “That is what you humans call us, yes.” 

“How are you speaking my language?” 

“We are taught many human languages during the cold-dark season.” 

“What’s the cold-dark season?” 

The mermaid didn’t immediately answer his question. Instead, he gave Shouyuo a weird look and cocked his head to the left. “The time when the ocean is dark and cold and too dangerous to go far from home. It should be obvious.” 

Shouyou was fascinated. He crawled even closer, then sat back on his heels when he was so close to the mermaid he could’ve reached out and touched him if he wanted to. But those sharp teeth and the death glare stopped him from reaching out. “Tell me more!” 

“You do not even know my name. Will your… mother? Will your mother scold you for talking to a stranger?” The mermaid seemed genuinely worried, glancing away on the word “mother.” He also said the word like it was completely alien to him. 

Laughing, Shouyou shrugged, and shook his head. “Mom will just think I’m making you up! You mermaids are just fairytales!” He sighed, a little dreamy. “She’ll just say I imagined you because I want something pretty to draw, that’s all.” Most of his drawings were of animals and plants, but sometimes he drew people, too. “Oh! And my name is Shouyou! What’s yours? If we know each other’s names, we won’t be strangers anymore!” 

The mermaid was obviously skeptical. But his eyes were glued to Shouyou’s, and he mouthed his name silently before giving his own. “Tobio,” he said. “My name is Tobio.” 

“Nice to meet you. Tobio!” Shouyou held out his hand for a handshake, but the mermaid, Tobio, just stared at it in mild horror. “It’s a handshake” he explained.“See, hold my hand with yours, and then you shake it! It’s a human greeting!” He wiggled his hand.

Tobio did not look convinced, but he sat up from his lying down position so both hands were free. Tentatively, he reached forward to cup Shouyou’s hand between both of his palms and then shook it from side to side. It was a little weird, but it was good enough. “You humans have strange greetings,” he muttered.

“How do you guys greet each other, then?” Shouyou was very curious, and he leaned forward towards Tobio, smile wide and bright. 

Without warning, the mermaid brought both hands up and placed them on his shoulders, pulling him forward until their foreheads were pressed together. Shouyou could only sit there in stunned silence, as one, two, three seconds passed. The mermaid’s eyes were squeezed shut, but Shouyou’s were wide open. When they parted, he rubbed the spot on his forehead Tobio had touched. 

“Wow! That’s a lot more personal than a handshake!” he laughed, but his voice was a little shrill and strained. The spot on his forehead was burning, and his shoulders were tingling. “Do you always do that? With everyone?” 

Tobio sat back with his hands propping himself up, his tail stretched out in front of him. “I would, yes. I am not around many strangers. I stay with my brothers. I am too young to leave them and find other pods.” 

There were so many questions swirling around in Shouyou’s head. But he focused on the simplest. “How old are you?” 

“One-hundred-and-thirty-nine moons,” Tobio answered, raising his chin up just a bit, a little proud. “I am very close to one-hundred-and-fifty!” 

“Moons…?” Shouyou was confused. “What are those?” 

“You know,” Tobio began, and he pointed up to the moon above them. It looked to be nearly full, but Shouyou couldn’t quite tell. “Moons. Each one is the full cycle. When the moon disappears, reappears, and disappears again. That is one moon.” 

So basically, moons were months. That sort of made sense. But Shouyou had to do a lot of math in his head to figure out how many years would go into that. After a moment of silence, he perked up. “So you’re about eleven and a half! Which means I’m older!” He grinned at Tobio. 

“Eleven and a half what? What are you measuring?” Tobio seemed both confused and annoyed, which made Shouyou feel sort of smug. 

“Well, you see, humans measure in lots of time! Seconds, minutes, hours, days, weeks, months-those are like your moons-and years! I am twelve years old!” He couldn’t hold up twelve fingers, but he held up two and flashed two fives at Tobio. That would work. 

This only seemed to confused the mermaid, as his lip twisted and his eyes narrowed to slits and he peered at Shouyou with a blank expression. “That is too many ways to divide time,” he muttered. “You humans are very strange.”

“We’re a bit weird, yeah!” he said. “But _you_ have the tail of a fish! That’s even weirder!” 

Tobio glanced down at his tail, and it flopped once, making a wet noise on the sand. “My tail is normal. It is still growing. My brothers have much prettier tails.”

That _had_ to be impossible. Tobio’s tail was the most beautiful thing Shouyou had ever seen in his entire life! 

“They are also all older than me,” Tobio added. “Their tails have been growing for longer. They have more fins than me, and my tail is still only one color.” He ran a finger with a slightly pointed nail tinted a light blue along his scales. Shouyou was itching to do the same. “My tail is still growing.” 

“So how many brothers do you have?” he asked. Subtly, he inched forward, since Tobio was focused on his tail. “Do they all look like you?” Were they all as beautiful? Shouyou wanted to hear everything. 

Tobio shook his head. “No, they do not all look like me. Keiji and Kenma have dark hair like me, but we do not look alike. I have six brothers. However, I think one of my brothers, Tooru, will be leaving soon. He has found his own mate.” 

A blush heated Shouyou’s cheeks at the word “mate.” His brother must be much older, because Tobio was still so young! A mate meant something like a husband or wife! “A m-mate?” he stammered, voice shaking. “Wow! That’s cool. Right?” 

Tobio looked a little sad, but he nodded. “It is a good thing. But we will miss him. I do not know how I will say goodbye to him.” 

Shouyou noticed Tobio’s hands were twisting together while resting on his tail. “Won’t you still see him?” 

“Most likely? No,” Tobio mumbled. “He is leaving the sea behind to be by his mate’s side.” 

“Oh…” Shouou understood now why he looked so sad. “But at least you have your other brothers! And your brother will be really happy, I think, so you shouldn’t be sad!” 

His words seemed to have some sort of influence, because Tobio gave him a very small smile. “Yes, that is what I tell myself. And the ocean will give me more brothers. We must keep the balance, and so there will always be many of us.”

Shouyou had no idea what Tobio meant by that, but it sounded nice and poetic, so he smiled and nodded. “Exactly! You have the right idea!” 

A small quiet stretched between them, where Tobio just looked out at the waves and Shouyou looked at Tobio. The mermaid seemed to refuse to look at him, focused on something far away. Shouyou still really wanted to touch Tobio’s tail, but he kept his hands to himself. Eventually, he too turned his gaze to the ocean. It was quiet and so very peaceful. 

They sat there for long enough that Shouyou’s legs started to go numb, but he didn’t want to disrupt the peaceful moment. So he sat as still as he could, which was very difficult for someone as energetic as Shouyou. But he also didn’t know if he would ever see Tobio again, or if this was even real. But he was also very bad at keeping quiet, and couldn’t help it when he turned to say, “Why are you here? Are you stranded or something?” 

Tobio looked at him, eyes a little wide, and his cheeks and ears turned a faint red. “N-no! I’m not stranded. I wanted to… bathe in the moonlight. And I was curious.” 

Shouyou chewed on his lip while he thought about Tobio’s answer, before nodding and turning back to look at the sea. The sound of the surf and the soft moonlight and the fact Shouyou hadn’t gotten enough sleep all started to make his eyes feel heavy, and he kept listing towards Tobio, before snapping back upright and shaking his head. After the fifth instance of this, Tobio looked at him, curious.

“Are you ill?” he asked.

“What no!” Shouyou yelped, shaking his head quickly. “I’m just sort of tired! I was sleeping, but then I woke up, I dunno why, and I came outside, and that’s when I found you! I’m usually sleeping at night like this, so being awake is kind of weird.” 

Tobio watched him with a wary eye. “You woke up? Was there some sort of noise?” 

Shouyou shook his head. “No, and it’s sad, cause I was having a cool dream, I think! I was underwater. It was awesome! But then I just woke up and felt the need to come out here, so… here I am! But I’m sleepy.” 

“You felt the need…” Tobio stopped speaking, still looking at Shouyou like he was trying to understand something. Then, all of a sudden, he lifted his hands from where they were resting on his tail and patted the empty space twice. “Lie down,” he said, but it sounded more like a command than anything else. “You can sleep here.” 

_“What?!”_ Shouyou was very shocked, staring at Tobio with his mouth hanging open.

“What?” Tobio snapped back. He jutted out his chest and crossed his arms in defiance. “I’ve seen you humans use each other for sleeping on. So just sleep! I will watch over you.” 

A mermaid offering Shouyou to sleep on his lap? Tail? Lap-tail? Shouyou was definitely dreaming. But if he was dreaming, that meant he would just wake up back in his bed, so it was perfectly safe. “Okay,” he decided. Hesitant, he reached out with one hand to lightly feel the scaly tail. It was warm, and moist, and very smooth. The scales were all flat against each other and felt smooth when he ran his palm across them. It felt sort of like the snake Shouyou’s mother let him hold once at the zoo. “Wow…” he whispered, mostly to himself, before stretching out and pillowing his head on his arms, curling up against the tail. It was oddly comfortable. 

“Now rest, little human Shouyou,” Tobio murmured, voice low and sweet and just a little bit soft. “You will be safe.” 

Shouyou hummed in contentment, closing his eyes and wriggling just a bit so he could get comfy. He stilled when he felt a hand land on his head, and then fingers were running through his hair, gently picking at the little snarls and knots. Pointy nails scratched lightly at his skull, and it was the best thing Shouyou had felt in his whole life. 

“G’night, Tobio,” he mumbled, before yawning once and then settling back down and letting out a big sigh. He didn’t hear Tobio’s response. 

Tobio kept his eyes on the waves until he was sure Shouyou was asleep. The human boy was dead to the world, snoring softly and drooling slightly on his arm. The mermaid’s hand stilled in the human boy’s hair, and he bent down to whisper something soft and sweet into Shouyou’s ear. Slowly and carefully, he moved his tail out from under Shouyou’s head and arms. Tobio was careful, making sure Shouyou didn’t wake up when he was laid on the bare sand. Then, as quietly as he arrived, he pulled the waves towards himself and slipped back into the water, glancing back at the shape of the sleeping human on the shore.

With a soft whisper and a longing look to the human boy now almost too far away to see, Tobio made sure to persuade the waves to look after Shouyou, so he wouldn’t be caught by the high tide in the morning and drown. And with that, the mermaid disappeared into the dark waters, leaving Shouyou fast asleep on the wet sand, bathed in moonlight and protected by the little waves dancing at the waterline. 

 

_"Please return to me."_

**Author's Note:**

> I KNOW IT WAS SHORT AND LAME BUT THERE'S MORE TO COME!! i already have the 1st chapter of the second part of this series completed, as well as about half of the second chapter. but i live off of validation, so... if u want more... comments make me literally tear up. if u subscribe to the series you should see the next part up within the next month or so!  
> i know the haikyuu fandom isn't as lively as it used to be, but i miss it so much! and i've written a couple kagehina fics in the past couple weeks, so check those out if you want!  
> tumblr is @4hoots, i am DESPERATE for friends  
> thank you for reading! <3


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